Most of the storage mites, booklice and house flies which can be seen in foods are associated with degradation of damp, dead plant material in nature. Different materials such as hay, straw, grain, flour, rapeseed and oats are infested by practically the same mould-eating insects. This is due to the fact that these insects are able to eat various types of mould. In feed compounds mould fauna is supplemented with species that are particularly favoured by the fat and protein content of these mixtures.
Mould pests never establish themselves in dry foods. They occur only in slightly mouldy foods containing too much water or humidity. Mould-eating pests are, like the fungi they eat, very numerous in Northern European nature.